Subject: Re: [PATCH net-next v8 0/4] send credit update during setting SO_RCVLOWAT

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 12 Dec 2023 10:54:50 -0500

On Tue, Dec 12, 2023 at 12:16:54AM +0300, Arseniy Krasnov wrote:
> Hello,
> 
>                                DESCRIPTION
> 
> This patchset fixes old problem with hungup of both rx/tx sides and adds
> test for it. This happens due to non-default SO_RCVLOWAT value and
> deferred credit update in virtio/vsock. Link to previous old patchset:
> https://lore.kernel.org/netdev/[email-masked]/

Patchset:

Acked-by: Michael S. Tsirkin <[email-masked]>

But I worry whether we actually need 3/8 in net not in net-next.

Thanks!

> Here is what happens step by step:
> 
>                                   TEST
> 
>                             INITIAL CONDITIONS
> 
> 1) Vsock buffer size is 128KB.
> 2) Maximum packet size is also 64KB as defined in header (yes it is
>    hardcoded, just to remind about that value).
> 3) SO_RCVLOWAT is default, e.g. 1 byte.
> 
> 
>                                  STEPS
> 
>             SENDER                              RECEIVER
> 1) sends 128KB + 1 byte in a
>    single buffer. 128KB will
>    be sent, but for 1 byte
>    sender will wait for free
>    space at peer. Sender goes
>    to sleep.
> 
> 
> 2)                                     reads 64KB, credit update not sent
> 3)                                     sets SO_RCVLOWAT to 64KB + 1
> 4)                                     poll() -> wait forever, there is
>                                        only 64KB available to read.
> 
> So in step 4) receiver also goes to sleep, waiting for enough data or
> connection shutdown message from the sender. Idea to fix it is that rx
> kicks tx side to continue transmission (and may be close connection)
> when rx changes number of bytes to be woken up (e.g. SO_RCVLOWAT) and
> this value is bigger than number of available bytes to read.
> 
> I've added small test for this, but not sure as it uses hardcoded value
> for maximum packet length, this value is defined in kernel header and
> used to control deferred credit update. And as this is not available to
> userspace, I can't control test parameters correctly (if one day this
> define will be changed - test may become useless). 
> 
> Head for this patchset is:
> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=021b0c952f226236f2edf89c737efb9a28d1422d
> 
> Link to v1:
> https://lore.kernel.org/netdev/[email-masked]/
> Link to v2:
> https://lore.kernel.org/netdev/[email-masked]/
> Link to v3:
> https://lore.kernel.org/netdev/[email-masked]/
> Link to v4:
> https://lore.kernel.org/netdev/[email-masked]/
> Link to v5:
> https://lore.kernel.org/netdev/[email-masked]/
> Link to v6:
> https://lore.kernel.org/netdev/[email-masked]/
> Link to v7:
> https://lore.kernel.org/netdev/[email-masked]/
> 
> Changelog:
> v1 -> v2:
>  * Patchset rebased and tested on new HEAD of net-next (see hash above).
>  * New patch is added as 0001 - it removes return from SO_RCVLOWAT set
>    callback in 'af_vsock.c' when transport callback is set - with that
>    we can set 'sk_rcvlowat' only once in 'af_vsock.c' and in future do
>    not copy-paste it to every transport. It was discussed in v1.
>  * See per-patch changelog after ---.
> v2 -> v3:
>  * See changelog after --- in 0003 only (0001 and 0002 still same).
> v3 -> v4:
>  * Patchset rebased and tested on new HEAD of net-next (see hash above).
>  * See per-patch changelog after ---.
> v4 -> v5:
>  * Change patchset tag 'RFC' -> 'net-next'.
>  * See per-patch changelog after ---.
> v5 -> v6:
>  * New patch 0003 which sends credit update during reading bytes from
>    socket.
>  * See per-patch changelog after ---.
> v6 -> v7:
>  * Patchset rebased and tested on new HEAD of net-next (see hash above).
>  * See per-patch changelog after ---.
> v7 -> v8:
>  * See per-patch changelog after ---.
> 
> Arseniy Krasnov (4):
>   vsock: update SO_RCVLOWAT setting callback
>   virtio/vsock: send credit update during setting SO_RCVLOWAT
>   virtio/vsock: fix logic which reduces credit update messages
>   vsock/test: two tests to check credit update logic
> 
>  drivers/vhost/vsock.c                   |   1 +
>  include/linux/virtio_vsock.h            |   1 +
>  include/net/af_vsock.h                  |   2 +-
>  net/vmw_vsock/af_vsock.c                |   9 +-
>  net/vmw_vsock/hyperv_transport.c        |   4 +-
>  net/vmw_vsock/virtio_transport.c        |   1 +
>  net/vmw_vsock/virtio_transport_common.c |  43 +++++-
>  net/vmw_vsock/vsock_loopback.c          |   1 +
>  tools/testing/vsock/vsock_test.c        | 175 ++++++++++++++++++++++++
>  9 files changed, 229 insertions(+), 8 deletions(-)
> 
> -- 
> 2.25.1